ova, and large-yellow ova. Female E. nana with a snout-vent greater than 26 mm carry large yellow ova, and are considered ready for oviposition. E. nana relies primarily on chemical cues rather than visual cues for association preference. Both males and females exhibit sexual discrimination, suggesting the seeking out of potential mates—a rare behavior among salamanders. In addition, female and intersexual pairs are found cohabiting more than male pairs, suggesting selective aggressive behavior. While natural courtship and egg deposition have not been observed and documented as of yet, eggs of similar species of salamanders are known to be deposited on single plants and stones about 24 hours after courtship. Depending on how light or dark the substrate is, E. nana can change its dorsal coloring from light tan to dark brown by migrating pigments in melanophores. The color of its gills also changes in response to the oxygen content of the surrounding water, where it appears bright red from increased blood flow in low-oxygenated waters to the point of resorption when kept at highly-oxygenated areas. Conservation status The San Marcos salamander has been federally listed as a threatened species since 1980. Due to its extremely limited geographic range, it is threatened primarily by the contamination of groundwater sources and heavy dependence of central Texas cities upon the Edwards Aquifer for water. Other threats include drying of the spring and introduced species. As migration cannot introduce genetic variation due to limited geographic range, the loss of genetic diversity cannot recover naturally when lost. Availability of food and sufficient prey also remain of concern for these salamanders, but less so than habitat loss or change. The San Marcos salamander and four other listed species are covered by the 1996 San Marcos/Comal (Revised) Recovery Plan, which includes recovery goals such as preserving the integrity and function of the aquifer and developing strategies to address both local and broad regional issues related to recovery. Experiments at the Dallas Aquarium were initiated to develop captive breeding techniques in case the natural population was lost. E. nana in captivity showed a 30% hatching success rate, with a single female producing potentially 176 eggs per year. Diseases Kyphosis due to microsporidia, intracellular protistan parasites, has been reported in captivated E. nana. Batrachochytrium dendrobatidis, a global threat to amphibians, has also been detected in E. nana. It causes chytridiomycosis and death in salamanders, and have lead to multiple